Coating material comprising linear isotactic polymers

ABSTRACT

The present invention relates to articles comprising elements at least partially coated with polymeric material wherein the structure of the polymeric material contains elastic amorphous areas of nano-scale-size reinforced with self arranged crystalline domains of nano-crystals. An article, comprising an element and a polymeric coating material covering at least portion of the surface of said element characterized in that said coating material comprises a polyolefinic homopolymer having an isotacticity of less than 60% of mmmm pentad concentration, is claimed.

FIELD OF THE INVENTION

The present invention relates to coating materials used for example ininsulation, shock absorption, cushioning, packaging. Specifically, thepresent invention relates to elastic coating materials.

BACKGROUND

Coated articles and in particular coating materials comprising olefinicpolymers are well known in the art and enjoy widespread usage throughoutthe industry. Typical areas of application of such coating materialinclude hygienic articles and in particular disposable absorbentarticles, packaging materials.

Coating materials made from commonly used polyolefins such as PP, PE, PSPIB have a number of useful properties. They are bio-compatible and foodcompatible, chemically stabile, inert, non toxic materials. However,most of them are rigid and have poor mechanical properties includinginsufficient strength/tear resistance, insufficientstretchability/elasticity and the like.

Several approaches have been proposed in the prior art to provideelastic properties to such polymeric coating materials. The mostcommonly used approach is based on changing the chemical structure ofthe polymer by introducing hinged joints/moieties into the main chain ofthe polymer. These hinges provide more flexibility to the polymericbackbone preventing crystallization of polymer, lowering the glasstransition temperature (Tg) and improving the elasticity of theresulting material. Usually, the hinge groups contain heteroatomsproviding flexibility such as oxygen, nitrogen or chlorine placed intothe main chain or into bulky side groups. Another approach ismastication of the polymer by blending with special plasticizing agents.Both approaches, however, require heteroatoms to be introduced into themolecule or into the bulk of the coating material.

The third approach proposed in the prior art to provide elasticproperties to such polymeric coating materials, which is more close tothe present invention, is to exploit the formation of hetero-phaseswhich reinforce the bulk material by forming a physical net. To do thisthe block-co-polymerization of two or more different monomers has beenused leading to polymeric backbones comprising blocks with different Tg.This results in micro-phase separation in the bulk with formation ofreinforcing crystalline domains of one co-polymer linked with each otherby flexible chains of the second co-polymer.

In essence, conventional polymeric coating material carry a wide varietyof inherent disadvantages including but not being limited toinsufficient strength/tear resistance, insufficientstretchability/elasticity, not being bio-compatible, not being foodcompatible, comprising heteroatoms such as chlorine and hence leading totoxic residues when burnt, and the like.

It is an object of the present invention to provide coating materialswhich overcome the disadvantages of the prior art coating materials.

It is an further object of the present invention to provide articleswhich comprise elastic coating materials.

It is an further object of the present invention to provide a method formanufacturing a coated article of the present invention.

SUMMARY OF THE INVENTION

The present invention provides a coating composition for covering atleast a portion of the surface of an element with a polymeric coatingcharacterized in that said coating composition comprises a polyolefinichomopolymer having an isotacticity of less than 60% of [mmmm] pentadconcentration.

The present invention further provides an article comprising an elementand the aforementioned polymeric coating material covering at leastportion of the surface of said element.

The present invention further provides a method for coating an elementwith the aforementioned polymeric coating material comprising a stepselected from the group of dip coating, spray coating, emulsion coating,and combinations thereof.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides coating materials comprising apolyolefinic homopolymer.

The present invention provides coating materials comprising apolyolefinic homopolymer.

The term “polyolefinic homopolymer” as used herein refers to thosepolyolefins which comprise only one phase of molecules all of whichexhibiting a similar stereochemical configuration. For example, blendsof atactic and isotactic polymers where the two phases have polymerizedsimultaneously are excluded when this term is used. The term homopolymerincludes copolymers where all molecules exhibit a similar stereochemicalconfiguration.

The polyolefinic homopolymer of the present invention may compriselinear isotactic polymers having a structure of one or several C₃ to C₂₀olefinic monomers, having an isotacticity of less than 60%, preferablyless than 55%, more preferably less than 50%, and most preferably lessthan 45% of [mmmm] pentad concentration, and having an isotacticity ofmore 15%, preferably more than 20%, more preferably more than 25%, andmost preferably more than of [mmmm] pentad concentration. Preferably,the polyolefinic homopolymer is polypropylene.

The isotacticity of the homopolymers may be reduced compared to theisotactic polypropylenes of the prior art due to a statisticdistribution of stereoscopic errors in the polymer chain. The term“stereoscopic error” refers to a stereoscopic sequence characterized bya [mrrm] pentad. In this case, the central monomer has a stereoconfiguration opposed to the other four monomers in this pentad. The[mrrm] pentad concentration of this polymer therefore is above thestatistical probability of p² (1−p)² where p=[m] and hence 1−p=[r] andp⁴=[mmmm]. Preferably, the pentad concentration is at least [p(1−p)]^(q) p (1−p) with q being 0.8, more preferably q being 0.6, yetmore preferably q being 0.4, yet more preferably q being 0.2, mostpreferably q being 0.1.

In some embodiments of the homopolymer and in particular in thoseembodiments where the crystallinity is reduced by means of single stereoerrors, a low content of atactic sequences has proven beneficial to theproperties of the coating of the present invention. Preferably, the[rmrm] pentad concentration is below 6%, more preferably below 5%, yetmore preferably below 4%, yet more preferably below 3%, most preferablybelow 2.50%.

In some embodiments of the homopolymer and in particular in thoseembodiments where the crystallinity is reduced by means of single stereoerrors, a low content of syndiotactic sequences has proven beneficial tothe properties of the coating of the present invention. Preferably, the[rrrr] pentad concentration is below 6%, more preferably below 5%, yetmore preferably below 4%, yet more preferably below 3%, most preferablybelow 2.5%.

Alternatively, the homopolymer of the present invention may includesequences of atactic and isotactic blocks of polymer. Preferably, themean molecular weight M_(w) of the polymer is above 100000 g/mol, morepreferably above 200000 g/mol, yet more preferably above 250000 g/mol,yet more preferably more than 300000 g/mol, most preferably more than350000 g/mol.

The glass temperature T_(g) is between −50 and +30° C. Preferably theglass temperature is below 10° C., more preferably below 5° C., yet morepreferably below 0° C., most preferably below −6° C. The melttemperature of the polymer is obtained after heating the sample 150° C.and subsequently cooling the polymer to −50° C.

Without wishing to be bound by this theory, the polyolefinic polymersexhibit a semi-crystalline structure. The structure contains elasticamorphous areas of nano-scale-size reinforced with self arrangedcrystalline domains of nano-crystals. The formation of brittlemacro-crystalline material from the polymer is achieved by introducingthe defects into the polymeric backbone. Isolated monomer units withopposite stereo configuration have been used as the defects, i.e. singlestereo errors.

Suitable polymers and a process for manufacturing such polymers aredescribed in PCT patent application EP99/02379 incorporated herein byreference. A catalyst combination suitable for the preparation of suchpolymers is described in PCT patent application EP99/02378 incorporatedherein by reference. Preferably, the process of PCT patent applicationEP99/02378 is carried out by temperatures of less than 30° C., morepreferably less than 25° C., yet more preferably less than 20° C., mostpreferably less than 15° C. to increase the molecular weight of theresulting polymer. In order to increase the molecular weight, thepolymerization is preferably carried out in liquid monomer such as inliquid propene. In order to increase the molecular weight, the catalystis preferably used in combination with the boron activators mentioned inPCT patent application EP99/02378.

Other suitable polymers and a process for manufacturing such polymers isdescribed in WO99/20664 incorporated herein by reference.

It is preferred to use homopolymers for the coatings of the presentinvention since during manufacture of homopolymers the batch to batchvariability is greatly reduced in comparison to multi phase polymerswhere the phases are polymerized in a single reaction.

Preferably, the polymers used in manufacturing the coating materials ofthe present invention have a distinctive rubber-elastic plateau in theirtensile-strength curves.

The polymers used for the coating of the present invention arebio-compatible may be burnt without toxic residues since they contain noheteroatoms such as chlorine. The further do not contain toxic monomerresidues.

The coating materials of the present invention have been found to beable exhibit superior softness. Preferably, the coating material has aShore hardness on the A scale of less than 30, more preferably, of lessthan 25, yet more preferably of less than 20, yet more preferably ofless than 15, most preferably of less than 10. The softness of thecoating material of the present invention can be increased bymanufacturing the coating by reducing the isotacticity ([mmmm] pentadconcentration).

The coating material has been found to exhibit increased temperaturestability compared to prior art coating materials. This is partly due tothe fact that for the coatings of the present invention a homopolymer isused and is partly due to the high molecular weight of the homopolymer.Preferably, the coating material of the present invention has a meltingpoint of at least 100° C., more preferably of at least 110° C., morepreferably of at least 120° C., most preferably of at least 130° C. Themelt temperature of the polymer is obtained after heating the sample150° C. and subsequently cooling the polymer to −50° C. Higher meltingpoint may be achieved my blending the homopolymer for example withconventional isotactic polymer such as polypropylene.

The coating of the present invention have been found to be stretchableas well as elastic. The stretchability of the coating versus its elasticbehavior can be adjusted by means of the tacticity of the homopolymer ofthe present invention. The coating material of the present invention hasbeen found to be stretchable without tearing to at least 500% of itsoriginal length, more preferably 1000% of its original length, yet morepreferably to at least 1500% of its original length, most preferably toat least 2000% of its original length. In addition, the coating materialof the present invention preferably recovers within 10 minutes afterbeing stretched and held for 1 minute to 500% of its original lengthback to less than 300% its original length, preferably less than 200%its original length, most preferably less than 150% of its originallength. In addition, the coating of the present invention has been foundto exhibit a low compressive set. The coating of the present inventionrecovers within 10 minutes after a compression to 50% of its originalthickness for 1 minute to at least 60% of its original thickness, morepreferably at least 70% of its original thickness, yet more preferablyto at least 80% of its original thickness, yet more preferably to atleast 90% of its original thickness, most preferably to at least 95% ofits original thickness. The compressibility of the coating of thepresent invention can be adjusted by increasing the tacticity of thehomopolymer or by blending the low tacticity homopolymer withconventional isotactic polymer such as polypropylene.

It has been found that the coating of the present invention can beapplied at relatively low basis weights. Preferably, the basis weight ofthe coating of the present invention is less than 50 grams per squaremeter, more preferably less than 40 g/m², yet more preferably less than30 g/m², yet more preferably less than 20 g/m², most preferably lessthan 10 g/m².

The coating of the present invention has been found to exhibit arelative low tackiness at room temperature due to the high molecularweight of the polymer.

Various additives may be added to the homopolymer of the presentinvention to change the properties of the polymer such as is well knownin the art.

It is a further aspect of the present invention to provide an articlecomprising an element, at least a portion of the surface the elementbeing covered with the coating material according to the presentinvention.

In the prior art, a wide variety of suitable techniques to manufacturecoating articles are known including but not being limited to dipcoating, spray coating, emulsion coating, and combinations thereof. Thecoating of the present invention is not limited to a specific substrateas long as the polymer of the coating is capable of sufficientlyadhering to the substrate material. Suitable substrates include but arenot limited to bodies of various material such as metal, polymer, wood,and the like, woven and nonwoven web materials, films, and the like. Theaforementioned methods for manufacturing coating articles all havespecific advantages which are known to the skilled person. Hence, theskilled person will be able to select a suitable method formanufacturing the coating material of the present invention depending onthe specific requirement of the respective application of the coatingmaterial.

In order to render the coating of the present invention breathable, thepolymer may be mixed with a particulate filler material such as calciumcarbonate prior to manufacturing the coating and be stretchedsubsequently (before or after contacting the substrate) in order tocreate micro pores at the location of the included filler material bystretching the coating material. Preferably, the breathable filmmaterial of the present invention has a moisture vapor transmission rate(MVTR) of at least 1000 g per 24 hours per square meter, more preferablyat least 2000 g/24 hours/m², yet more preferably at least 3000 g/24h/m², most preferably at least 4000 g/24 h/m². The method of determiningMVTR is well known in the art and should be applied accordingly.

The coated article of the present invention could be a hygienic article.The term “hygienic article” as used herein refers to articles which areintended to be used in contact with or in proximity to the body of aliving being. Such hygienic articles may be disposable or intended formultiple or prolonged use. Such hygienic articles include but are notlimited to gowns, surgical drapes, body implants, instrumentation,support means, bed covers, wound coverings, wound sprays, hair sprays,and the like. Having regard to the specific advantages of the polymersused for the articles of the present invention, it will be readilyapparent to the skilled practitioner to apply the coatings of polymericmaterial according to the present invention in the above and similarhygienic articles.

The coating material according to the present invention may also be usedas a construction element in an article. Thereby, the functionalities ofthe coating material includes but is not limited to heat insulation,electric insulation, shock absorption, cushioning, acoustic wavedamping, protecting other elements of the article, corrosion protection,allowance for relative movement of other elements, slip reduction, andthe like. Such articles include but are not limited to toys, furniture,clothing, shoes, sport equipment, grips, complex constructions such asbuildings (floor coverings, caulking, sealants, ridge/crack filler, andthe like), cars, household appliances, and the like. Having regard tothe specific advantages of the polymers used for the articles of thepresent invention, it will be readily apparent to the skilledpractitioner to apply and to optionally modify the coating materialsaccording to the present invention as construction elements in the aboveand similar articles.

What is claimed is:
 1. An article comprising an element and a polymericcoating material covering at least portion of the surface of saidelement characterized in that said coating material comprises apolyolefinic homopolymer having one phase of molecules all of whichexhibit a similar stereochemical configuration and having anisotacticity of less than 60% of [mmmm] pentad concentration, a [rmrm]pentad concentration below 3%. and a [rr] pentad concentration below 6%.2. An article according to claim 1 wherein said polymeric coatingmaterial is stretchable.
 3. An article according to claim 2 wherein saidcoating material is elastically expandable.
 4. An article according toclaim 1 wherein said homopolymer is polypropylene.
 5. An articleaccording to claim 1 wherein article is a hygienic article.
 6. Anarticle according to claim 1 wherein said polymeric coating is aconstructional element of the article.
 7. A method for coating anelement with a polymeric coating material comprising a step selectedfrom the group of dip coating, spray coating, emulsion coating, andcombinations thereof, characterized in that said polymeric coatingmaterial comprises a polyolefinic homopolymer having one phase ofmolecules all of which exhibit a similar stereochemical configurationand having an isotacticity of less than 60% of [mmmm] pentadconcentration, a [rmrm] pentad cocentration below 3%. and a [rr] pentadconcentration below 6%.